The present invention relates to paints and protective coatings, and particularly to a paint coating to prevent fungal or microbial growths.
In the past, toxic materials for control of microbial growth generally have been added to alkyd coatings as "external biocides" rather than chemically combining them with alkyd polymers to make them "internal biocides". The current practice of merely adding biocides to alkyd resins for control of fungal growth permits rapid loss to the environment resulting in loss of protection and contamination of the environment. By combining the biocide chemically to the resin, smaller amounts of biocide are required and its release controlled, thus achieving longer protection without as much adverse effects.
In the old procedures with added biocides for use in alkyd paints in tropical or other geopgraphical areas where fungal or other microbial growths were a problem, the toxic "external biocides" were hazardous to handle, were frequently lost rapidly by leaching with rainwater or by volatilization, thus limiting their period of protection, or contaminated the environment in quantities which might produce adverse ecological effects. The new "internal biocides" are required in lesser quantities and are released at a much lower, controlled rate, thus retarding microbial growths for longer periods of time and constituting a lesser health or enviornmental hazard.
Prior coatings, particularly those for antifouling purposes, require high tin content (more than 5% by weight) and an alkyd resin value larger than 20, and also require that free (unreacted) carboxyl groups be present by using less than an equivalent amount of organotin compound. The present invention, however, is for a resin for paints used on atmospheric exterior surfaces where fungal or other microbial growth is a problem. This invention requires a much smaller tin content (e.g., 2% by weight), and is normally achieved using alkyd resins with an acid value less than 20 and by reacting it with an equivalent amount of the organotin compound so that no free carboxyl groups are present.
A primary purpose of the invention is to incorporate by chemical reaction a biocidal material into an alkyd proctective coating polymer as an actual chemically-bound component of the polymer rather than merely as an additive for use in a finished paint coating to prevent fungal or other microbial growth on buildings and other structures.
A further embodiment of this invention reacts organotin compound with a free vegetable oil acid and combines the reaction product with an alkyd resin (either reacted or unreacted with tin) to form a variety of compositions that will cure in air as hard biocidal paint films.